Stimulated erythropoiesis in mice infected with viruses encoding tyrosine add-back mutants of the EPOR. (A) Immediately before termination, hematocrits were determined for each animal infected with viruses encoding the indicated cEPOR variants. Each symbol represents a value from an individual animal, and the dashed line indicates the normal hematocrit of an adult mouse. (B) Immunoblot analysis for expression of the transduced EPOR protein in primary spleen cells isolated from infected mice.